The present invention relates to techniques for obtaining and analyzing blood samples, and more particularly to techniques for storing lancets that can be used for obtaining and analyzing blood samples in a convenient manner.
The analysis and quantification of blood components is an important diagnostic tool for better understanding the physical condition of a patient. Since adequate noninvasive blood analysis technology is not currently available, blood samples still need to be obtained by invasive methods from a great number of patients every day and analyzed. A well known example of such needs is self monitoring of glucose levels by a diabetic individual, e.g., performed at home. Many products for self monitoring of blood glucose levels are available commercially. Upon doctors"" recommendations and using such products, patients typically measure blood glucose level several (3-5) times a day as a way to monitor their success in controlling blood sugar levels. For many diabetics, the failure to test blood glucose regularly may result in damage to tissues and organs, such as kidney failure, blindness, hypertension, and other serious complications. Nevertheless, many diabetics do not measure their blood glucose regularly. One important reason is that the existing monitoring products may be complicated, inconvenient, and painful, requiring a pin-prick every time a measurement is made. Furthermore, these products require some skill, dexterity, and discipline to obtain useful measurements.
Today, a diabetic patient who needs to monitor and control blood glucose levels typically carries the following paraphernalia: (1) a supply of disposable lancets, (2) a reusable lancing device which accepts the lancets, (3) an electronic glucose meter (glucometer), (4) a supply of disposable glucose test strips for the meter, and (5) tools for insulin injection (insulin, disposable hypodermic needles, and a syringe). These items may be carried in the form of a kit, which may also contain (6) a variety of control and calibration strips to assure the accuracy of the meter and the measurement. Examples of devices for monitoring blood glucose include GLUCOMETER ELITE glucose meter, Miles Inc. Elkhart, Ind., and ONE TOUCH PROFILE glucose meter, Lifescan Inc., Milpitas, Calif.
Using a typical glucose meter and lancing device, the sampling and measurement process is generally as follows. First, the user prepares the meter for use by removing a test strip from a protective wrapper or vial and inserting the test strip in the meter. This simple process requires some dexterity, since the test strips are very small, flexible, and can be damaged by accidentally touching the active sensing region. The glucose meter may confirm the proper placement of the test strip and indicate that it is prepared for a sample. Some glucose meters also may require a calibration or reference step at this time. Next, the patient cleans his finger when he intends to use the lancetxe2x80x94the finger is the preferred place for routine sampling, because it is an easily accessible place for most people. The user prepares the lancing device by (1) removing a cover from the lancing device, (2) placing a disposable lancet in the lancing device, (3) removing a protective shield from the sharp lancet tip, (4) replacing the cover, and (5) setting a spring-like mechanism in the lancing device which provides the force to drive the lancet into the skin. These steps may happen simultaneously, e.g., typical lancing devices set their spring mechanisms when one installs the lancet. The user then places the lancing device on the finger. (The density of nerve endings decreases toward the lateral edges of the fingertips; thus, slightly lateral locations are preferred to the fingertips.) After positioning the lancing device on the finger, the user presses a button or switch on the device to release the lancet. The spring drives the lancet forward, creating a small wound.
After lancing, a small droplet of blood may appear spontaneously at the lancing site, usually 2-20 xcexcl in volume. If no blood sample appears spontaneously, the patient may xe2x80x9cmilkxe2x80x9d the finger by massaging or squeezing it slightly and thereby promoting blood flow from the wound. In either case the user examines the droplet of blood, judges by eye and experience whether the size of the sample is adequate for the chosen test strip (different test strips require different sample volumes). If adequate, the user quickly places the blood sample on a test strip (held in the glucose meter) according to manufacturer""s instructions. Typically, the user inverts the finger to create a pendant drop and touches the drop (not the finger) to. an active region on the test strip that absorbs the blood. The action is difficult because inverting the finger over the test strip occludes the view of both the drop and the active region of the test strip. Furthermore, it is difficult to control the separation between the finger and the test strip which may be only a millimeter. Certain types of strip may require blotting and rubbing in a particular way. Another type of test strip draws the sample into the active region by capillary action. With this type, the user brings the sample in contact with a small opening on the test strip, and capillary action draws the sample volume into the test strip. Both types of strips (absorbent blots and capillaries) require that adequate sample volumes of blood exist on the finger before transferring the sample to the strip. One cannot apply more drops after the first application. This is because the principle of glucose measurement methods using current glucose meters depends on the rate of change in a chemical reaction, and the addition of additional sample confounds that rate and thus the calculation of glucose concentration. For convenience to the patient (user), it is desirable to have the entire droplet wick away from the finger onto the test strip, leaving the finger mostly free of blood. This is easier to accomplish with the capillary-fill test strips. The GLUCOMETER ELITE device has capillary-fill type test strips which require a few microliters of sample, only some fraction of which contacts the active sensor region.
After blood has been transferred to the test strip, the glucose meter then measures the blood glucose concentration (typically by chemical reaction of glucose with reagents on the test strip). Such blood glucose measurements permit the diabetic to manage his glucose levels, whether that be to inject a corresponding dose of insulin (generally Type I diabetic) or using a protocol established with his physician to modify his diet and exercise (Type I or Type II diabetic). Used lancets and test strips are removed and discarded (or kept for subsequent disposal in a hazardous waste container kept elsewhere). Any extra blood is cleaned from the equipment and the wound site, and all pieces of apparatus are stored for future use. The entire process usually takes a few minutes.
With the currently available blood glucose monitoring technology, a new lancet and test strip are used every time. The lancet and test strip are separate items, often purchased from different manufacturers. Furthermore, both are protected by a package or a protective shield, which must be removed before use, adding the requirement for dexterity. Because both are exposed to blood (considered a bio-hazard) they require careful or special disposal.
Each lancet prick causes pain. Among other considerations, pain from the lancet corresponds to the size of the wound, for a given location on the finger. A small lancet wound, which may cause less pain, may not provide enough blood for a sample, while a large wound may produce considerable pain and may clot slowly, causing great inconvenience to the user, who must take great care not to smear the leaking blood everywherexe2x80x94clothes, work surfaces, glucometer, etc.xe2x80x94for some time thereafter.
From the above, it is clear that the conventional technique for blood sampling and analysis requires dexterity. Dexterity is required to load strips in a glucometer (unwrapping and inserting), as well as for positioning a small droplet onto the sensor surface of a test strip. Sample droplets are a few millimeters across and must be placed on similarly sized area of the test strip. This can be especially difficult for a weak, chronic or elderly diabetic patient, whose motions may be unsteady, vision compromised, or judgment impaired. Thus, the above prior systems are inconvenient and unpleasant to use. These shortcomings reduce the level of compliance of patients who need to perform these measurements assiduously.
Therefore, it is desirable to devise techniques of blood extraction and measurement that are easy to administer. What is needed are improved devices and methods for sampling and analyzing blood that require less mental concentration, less exertion, and less dexterity.
This invention provides techniques for extracting a sample of human blood for the measurement of one or more of its constituents, such as might be used for routine monitoring of a chronic condition such as diabetes mellitus. The techniques of the present invention simplify the extraction and transfer of the blood sample, and reduce the inconvenience of the process. The techniques can be advantageously used in, for example, blood glucose monitoring as explained above.
In one aspect of the present invention, a cassette is provided for storing cartridges which can be used for sampling blood from the skin of a patient. The cassette has a cassette housing, i.e., a container, with room to hold a plurality of cartridges. When in use, the cassette contains at least one cartridge having a cartridge case and a lancet. The lancet has a tip and is housed in the cartridge case and operatively connected to the cartridge case such that the lancet can be driven to extend the tip outside the cartridge case for lancing the skin of the patient. The container has a compartment for storing at least one, but preferably many, cartridges. Alternatively many compartments can each contain one cartridge. A cartridge can be loaded from the cassette to a glucometer that can drive the lancet to lance the skin of a patient. In an preferred embodiment the cassette is associated with the driver so that the driver can be used to drive different cartridges of the cassette without having to remove the cassette from the glucometer. By keeping the cartridges, cassette, and the glucometer together, the process of lancing the skin is significantly simplified.
In an embodiment of the present invention, the technique of sampling blood utilizes a single unit for lancing and measurement (versus separate lancers and meters as in methods of prior technology) to significantly reduce the assortment of devices and supplies the user must carry. The glucometer of the present invention can accept a pre-loaded number of cartridges (with lancets) that are ready for use. In a preferred embodiment, the lancet and the analysis site for blood are in the same cartridge, further increasing the convenience of use. Using the blood sampling and analysis devices of the present invention, unlike the procedures used in conventional technology, the long list of steps required is significantly reduced. For example, after lancing, there is no need to return the package of lancet and the glucometer to storage separately. When the time for the next lancing arrives, there is no need to fumble for the lancet, lancing device and glucometer separately. Furthermore, the cassette can provide a convenient place for storing spent (i.e. used) cartridges, thereby facilitates easy disposal of spent cartridges and reduces the risk of blood contamination to others.